Even in years when flu vaccines have reduced efficacy, experts say flu shots are a safe and easy way to reduce one's chances of getting sick and spreading the flu. (U.S. Air Force photo/Senior Airman Areca T. Wilson)

Even in years when flu vaccines have reduced efficacy, experts say flu shots are a safe and easy way to reduce one's chances of getting sick and spreading the flu. (U.S. Air Force photo/Senior Airman Areca T. Wilson)

HOUSTON— A Rice University study predicts that the 2018 fall flu vaccine will have little effect against influenza A as the vaccine given in 2016 and 2017 due to viral mutations related to vaccine production in eggs.

The Rice method, known as pEpitope was invented more than 10 years ago as a fast, inexpensive way of gauging the effectiveness of proposed flu vaccine formulations. In the new study, the method accurately predicted vaccine efficacy rates for more than 40 years of flu records. These included the past two flu seasons in which vaccines offered only limited protection against the most widely circulating strain of influenza A.

“The vaccine has been changed for 2018-19, but unfortunately it still contains two critical mutations that arise from the egg-based vaccine production process,” said Michael Deem, Rice’s John W. Cox Professor in Biochemical and Genetic Engineering and professor of physics and astronomy. “Our study found that these same mutations halved the efficacy of flu vaccines in the past two seasons, and we expect they will lower the efficacy of the next vaccine in a similar manner.”

Michael Deem and Melia Bonomo (Photo by Jeff Fitlow/Rice University)

Full efficacy data for the 2017-2018 flu season are still being compiled, but pEpitope has predicted it will be around 19 percent against H3N2, the type of influenza A that infected most people in the U.S. in each of the past two years. The Food and Drug Administration chose the same vaccine formulation in 2017 and 2016, in part because the dominant circulating strain stayed the same. In 2016, the vaccine had an efficacy of 20 percent, almost identical to the efficacy of 19 percent predicted by pEpitope.

A 20 percent efficacy means that in a population, 20 percent fewer vaccinated people will get the flu compared to the unvaccinated people.

Most flu vaccines are produced with a decades-old process that involves culturing viruses in hundreds of millions of chicken eggs. Because the strain of flu that infects people is often difficult to grow in eggs, vaccine producers must make compromises to produce enough egg-based vaccine in time for fall flu shots.